What is known as apparatuses for purifying water by increasing its dissolved oxygen concentration are those disclosed in Japanese Utility Model Registration Laid-open No. 6-57500 and Japanese Patent Laid-open No. 56-58526. Such water purification apparatuses have structures wherein water fed from an underwater pump is rapidly jetted out of a nozzle built into an ejector, thereby creating negative pressure in the vicinity of the nozzle and attracting air to the nozzle because of the negative pressure. As air and water are mixed to dissolve the oxygen into the water, a jet flow of air and water in a mixed state is ejected from a jetting outlet on the edge of a tubular body connected to the ejector. In these conventional water purification apparatuses, diffusion of a jet flow is facilitated by installing a jetting outlet nozzle having openings disposed radially or by placement of a curved plate.
In addition, as a water purification apparatus equipped with a biological filter in addition to the above-mentioned oxygen supply device, an apparatus disclosed, for example, in Japanese Patent Laid-open No. 4-346897 is known. This apparatus uses ammonia-oxidizing bacteria or nitrous acid-oxidizing bacteria, which are aerobic bacteria, disposed on a surface of the biological filter, and thereby oxidizing, in an oxygen-rich atmosphere, noxious ammonia or nitrous acid produced as a result of decomposition of organic materials, to change it to nitric acid which has no toxicity to fish.
In the above, the biological filter functions to purify water but will not play a role for activating water. Activation of water is obtained by non-thermally exerting thereon various energies such as an electric field or magnetic field at a low level, thereby causing changes in properties of water such as a decrease in oxidation-reduction potential, an increase in interfacial activity, and a decrease in surface tension so as to give water a purification function. In general, water subjected to such functioning treatment tends to have a high pH.
As an apparatus for both purification and activation of water, the one disclosed in Japanese Patent Laid-open No. 7-16598 is known. This apparatus is so structured that water to be treated flows in the state of a jet flow through the interior of a pipe where a magnetic field is formed by a magnet. The magnetic field discharges colloid particles, which makes easy the coagulation and sedimentation of clay, iron components, manganese, silicic acid component, sludge, or the like.
In the conventional water purification apparatuses, air sucked into an intake pipe collides, at a downstream of an ejector, against a water flow, thereby breaking down air bubbles and inducing the oxygen to dissolve in water. However, in the structure used in the conventional water purification apparatuses, because the jet flow of air and water in the mixed state is discharged immediately from the jetting outlet, formation of minute air bubbles does not sufficiently progress, and thus an increase in oxygen dissolution cannot reasonably be expected.
On the other hand, when increasing the amount of oxygen dissolution in order to purify water, water becomes acidic and is likely to realize an adverse effect on components in the apparatuses such as a pipe. Thus, in the conventional water purification apparatuses, adjustment of pH of water is conducted by adding chemicals. However, such water treated with chemicals has a problem in safety. In addition, in conventional apparatuses for purification and activation of water, a ring-shaped permanent magnet is used. However, activation with a magnetic field cannot result in production of water having a sufficient interfacial activation function, and it is difficult to adjust the pH of water.